Four children were burned and taken to the hospital after an incident on a bus from the Institute for Development of Young Leaders in Durham. It happened Monday afternoon on Angier Avenue and South Hoover Road in east Durham.

The fire department said the bus radiator overheated and hot liquid leaked into the passenger compartment.

"A radiator hose or a component of a radiator spewed a small amount of anti-freeze into the passenger cabin of the bus, injuring four students who were seated in the very back of the bus," explained Christopher Edwards, chairman of the charter school's board.

All of the injured students were taken to Duke University Medical Center. The injured students range in age from kindergarten to fifth grade.

One of them is at home recovering, according to their mother who asked ABC11 not to identify her or her child.

"He knew something was wrong with the bus," she said. "He knew that once something wrong happened. He knew he had to help his friends."

School leaders with the Institute for the Development of Young Leaders said an internal investigation is underway to find out exactly why the radiator ruptured.

The bus is owned by Frontline Quality Transportation. School officials say the company inspected the bus just five days before the incident.

Because it is a charter school, it isn't subject to annual state inspections.

"In addition to having a very rigorous preventive maintenance program to try to protect that fleet, we also ask that the buses are inspected every 30 days," explained Derek Graham with the Department of Public Instruction.

Public school systems have to follow that rule but not private or charter schools. That's why the state offers courtesy inspections but there's no record of such inspection at the Institute for the Development of Young Leaders.

ABC11 contacted the company that owns the bus but got no response.

School officials told ABC that until yesterday, that bus had no other major incidents.

The mother of one of the young burn victims said it could've been much worse.

"I just want to thank the administration, the bus driver, the other kids, and everyone who helped get the kids off of the bus," she said.

School officials say three students remain at the UNC Burn Center.

Two are expected to return home this week. The fourth will undergo surgery for second degree burns.